This application claims the priority of Japanese Patent Application No. 9-325404 filed on Nov. 11, 1997, which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to an image readout apparatus such as copier, facsimile machine, or image scanner; and, in particular, to an image readout apparatus which reads out color and monochrome images by means of several pieces of linear imaging elements.
2. Description of the Prior Art
There has conventionally been known an image readout apparatus which can read out both color and monochrome images by means of three CCD lines. Such an image readout apparatus reads out monochrome images by using one of the three CCD lines.
Since an imaging device for reading out colors separately captures three color light images by using three CCD lines, the surface of each element of CCD is coated with a filter having a wavelength characteristic for its corresponding color, which restricts the readable wavelength range, whereby the quantity of light reaching into each element would become smaller.
In a simple way of reading out monochrome images, one of the CCD lines for blue, green, and red has been used. In this case, however, the readable light wavelength range would become narrower than that in the case where a dedicated CCD line for reading out monochrome images is provided, thus greatly reducing the total readout light quantity. Hence, when reading out a monochrome image from a color original, the degree of contrast may vary depending on the color of the original.
Since making the readout speed higher when reading out monochrome images than when reading out color images would decrease the readout light quantity, it has been difficult to improve the readout speed without carrying out any particular modification of design such as an increase in the light quantity of light source.
It is an object of the present invention to provide an image readout apparatus which can read out both color and monochrome images by using a plurality of imaging element lines, wherein the readout speed for monochrome images can be made as fast as that in a dedicated apparatus for reading out monochrome images, while using only the imaging element lines used for reading out color images.
The image readout apparatus in accordance with the present invention comprises a light source for illuminating an original, an imaging lens for forming an image of the original illuminated by the light source, and at least three imaging element lines for reading out the image of the original formed by the imaging lens, wherein at least two of the imaging element lines have readout sensitivities for first and second visible light wavelength regions which are different from each other, at least one of the remaining imaging element lines has no specific wavelength selectivity in a visible light wavelength region, and respective image information data of three colors for forming a color image and a monochrome image information data are obtained according to output values from the at least three imaging element lines and a computed value based on the output values.
Also, the image readout apparatus may be configured such that three of the imaging element lines are formed as one set on an imaging device, two of which have sensitivities for two respective color light components, different from each other, selected from red, green, and blue, and the remaining imaging element line has no specific wavelength selectivity in the visible light wavelength region.
Further, in this case, the image readout apparatus may be configured such that, letting the respective outputs from the two imaging element lines be A and B, and the output from the remaining imaging element line be Z, the color light component not outputted from the two imaging element lines among red, green, and blue is obtained according to an arithmetic expression of KzZxe2x88x92(KaA+KbB), where Kz Ka, and Kb are constants appropriately determined according to the output levels of the respective imaging element lines.